Surface Runoff Sedimentation

Surface runoff transports sediment particles from the land into adjacent coastal waters. This process is primarily driven by intense rainfall, which generates overland flow toward the coast. As runoff moves across the land surface, it entrains soil and sediment particles and carries them into rivers and eventually to the coastal environment. Land-use changes, particularly vegetation clearing for agricultural development, significantly increase sediment loads entering the marine environment. The resulting impacts may include marine organism mortality, biodiversity loss, navigation hazards caused by shoaling, habitat degradation or loss, reduced natural seafood resources, changes in sediment grain-size distribution, increased water turbidity, and alterations in seabed depth.

Numerical modeling provides an effective means of simulating the entire sediment transport process, beginning with increased rainfall, overland runoff, river flow, sediment transport across the land surface and river channels, and finally the distribution of bed sediment and suspended sediment within coastal waters. Modeling scenarios are developed based on rainfall intensity, topographic characteristics, and surface soil types.

The modeling framework typically integrates the Land Flood and River Flow modules to simulate overland runoff, river discharge, and sediment transport within terrestrial and fluvial systems. The Hydrodynamic module is used to simulate coastal circulation and water level variations, while the Bed Sediment Transport and Suspended Sediment Transport modules simulate sediment dispersion and deposition in the marine environment.

Model modules applicable for surface runoff sedimentation studies include: